After successfully upgrading from an iPhone 5 to an iPhone 6, I had all my contacts on my iPhone.

I added a new contact to the iMac one evening and next morning it appeared in Contacts on my MB Pro, but not in Contacts on either my iPhone 6 or my iPad mini.

So, on the iPhone, I went to Settings > iCloud and turned off Contacts.

I got the alert: Delete Contacts from this iPhone or Save Contacts on this iPhone. I unwisely chose Delete and now no matter what settings I turn on/off followed by restarts, I cannot get my Contacts.app on the iPhone to repopulate with my contacts from iCloud.

Learning from my mistake, when I saw that this new contact had not appeared in Contacts on my iPad, I went to Settings > iCloud and turned off Contacts but this time chose Save Contacts to my iPad.

When I turned contacts back on in Settings > iCloud, one of the choices was Merge. I chose it and when I checked my Contacts on the iPad, all my contacts, including the new one I added via the iMac.

SO, question is, what settings do I have to change/what do I have to do to get my contacts to reappear on my iPhone 6?

The correct choice was to delete from my phone. Then when you turn contacts back on, they come back from the back up in iCloud. Not sure what all you did. They should still be in iCloud. When you toggle contacts on in iCloud on your phone, they should appear. That's how I thought it worked. I lost a bunch of contacts after the last update. I went to iCloud and contacts were toggled on. I toggled them off, chose "Delete from my phone", then toggled contacts back on. They reappeared in my contacts list. IDK!

As you suggested, with my iPhone 6 in front of me and while reading your reply on my MB Pro, I scrolled to the bottom of Settings > iCloud > and tapped Sign Out and when I saw the alert that said doing so would wipe out, among other things, Apple Pay and the data for the two credit cards I had entered, it made me pause and think about it for several minutes.

The iPhone screen dimmed, then shut off as is normal when it's been sitting with no input and at the same time, on my MB Pro I got a warning I have never seen before in fifteen years of using multiple Mac computers: Your system has run out of application memory. To avoid any problems with your computer, quit any applications you are not using. This on a MB Pro with 8GB of memory and only four or five apps open: Safari, Mail, NetNewsWire, and 1Password.

I launched Activity Monitor and saw that the Memory Pressure reading was almost topped out whereas, normally, it barely shows at the bottom. I quit all running applications and did a restart, following which, for some unexplained reason, I had to sign back into my iCloud account, my Messages account, etc.

When I got back to the desktop on the MB Pro, I went to the iPhone and cancelled signing out from iCloud and, for the heck of it, opened Contacts on the iPhone.

Everything was restored and even the new address I had added last night is also there.

So, through some weird magic I certainly don't pretend to understand, all is back to normal.

Any comments or observations anyone would like to make on this would be very welcome.